feat: add more robust tests

- add test to cover corner cases and known failure points

Signed-off-by: Avinal Kumar <avinal.xlvii@gmail.com>

tests/test_vectors.cpp

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2025 Avinal Kumar avinal.xlvii@gmail.com
+// SPDX-License-Identifier: MIT
+
+#include "test_framework.h"
+#include <blowfish/blowfish.h>
+
+// Known Answer Tests (KAT): Validate Blowfish output against fixed reference
+// vectors to ensure algorithmic correctness.
+TEST("Blowfish Known Test Vectors") {
+  Blowfish bf("abcdefghijklmnopqrstuvwxyz");
+
+  uint32_t L = 0x424C4F57; // "BLOW"
+  uint32_t R = 0x46495348; // "FISH"
+
+  bf.encrypt(L, R);
+  EXPECT_EQ(L, 0x324ED0FE);
+  EXPECT_EQ(R, 0xF413A203);
+
+  bf.decrypt(L, R);
+  EXPECT_EQ(L, 0x424C4F57);
+  EXPECT_EQ(R, 0x46495348);
+}